1. Field of the Invention
The invention relates to a stretching machine for webs of textile material with a driven drawing-in cylinder and chain tracks which are pivoted in the feeding region of the machine about vertical axes, the chain tracks being mutually and adjustably spaced apart for accomodating endless needle chains reversed or deflected for running into and out of the web of material, and a needle-engagement device at each chain track downstream of the drawing-in cylinder, as seen in the direction of the travel of the web.
2. Description of the Related Art
The entrance or feeding region of such a machine, which is also referred to as a tenter frame in the art, is described in German Published, Non-Prosecuted Application No. DE-OS 22 08 756. The drawing-in cylinder is customarily supported at the entrance of the machine frame. The operator of the machine normally stands on the side of the drawing-in cylinder facing away from the entrance area in such a way that he or she can survey the drawing-in area and particularly the needle engagement operation. If the needle engagement of the web of material is initially made improperly, it is sometimes even necessary to render assistance manually. For this reason, it is desirable to maintain the distance from the needle engagement point to the position of the operator and therefore the distance between the chain reversal wheel (of the entrance area) and the drawing-in cylinder, as small as possible. In the machine known from German Patent DE-PS No. 22 08 756, the entrance cylinder is brought so close to the needle engagement rolls of the needle engagement device that it can serve directly as the feeding element and even as the drive element for the needle engagement rolls. It is a disadvantage of the prior art machine that the lengthening of the chain and the chain track caused by wear of the pins and thermal expansion, which can increase up to the length of a chain link (since one chain link is removed if the lengthening is greater) cannot normally be compensated in the entrance or feeding area. This is because the maneuvering space required therefor is not available, since the distance between the drawing-in cylinder and the needle engagement point is set at a minimum.
In the journal "Textilveredlung" 13 (1978) page 319, a report is given regarding a stretching machine with a vertically deflected chain, the chain stretching means of which are disposed in the delivery or end area, so that the distance between the drawing-in cylinder and the needle engagement point is to remain constant. In this connection, the fact that the chain track itself has thermal expansion which, depending on the entire installation, is in general between 50 and 100 mm, is not taken into consideration. The distance between the drawing-in cylinder and the needle engagement point therefore varies by at least this amount even if some length change of the chain itself is compensated in the exit area of the machine. This difficulty could be counteracted if the fixed point of the chain track were placed as close as possible to the entrance area and in particular to the area of the vertical pivot axes of the chain track which delineate the entrance from the remaining part of the web. However, other disadvantages would again become more significant.
On one hand, the entire length change of the chain and the train track would be shifted into the exit region, so that the chain drive normally provided at this point would have to be movably supported. On the other hand, the chain tracks and the treatment chamber of the stretching machine would have fixed thermal-expansion points that would be different from each other, so that the fastening of the chain track within the chamber would become accordingly difficult.